I've been given a pair of bar ends - Bontrager ski - but I'm not sure how to fit them. They have what seems to be the standard bolt and clamp fitting. My handlebars and grips look pretty ordinary too. So, do I need to remove anything from the handlebar or do I just fit the clamp over the top of the grip? Should I buy a new grip or try to roll it back to expose the tube of the handlebars?